ABSTRACT
MATLAB
/ SIMULINK implementation of the Direct Torque Control Scheme for induction
motors is presented in this paper. Direct Torque Control (DTC) is an advanced
control technique with fast and dynamic torque response. The scheme is
intuitive and easy to understand as a modular approach is followed. A
comparison between the computed and the reference values of the stator flux and
electromagnetic torque is performed. The digital outputs of the comparators are
fed to hysteresis type controllers. To limit the flux and torque within a
predefined band, the hysteresis controllers generate the necessary control
signals. The knowledge about the two hysteresis controller outputs along with
the location of the stator flux space vector in a two dimensional complex plane
determines the state of the Voltage Source Inverter (VSI). The output of the
VSI is fed to the induction motor model. A flux optimization algorithm is added
to the scheme to achieve maximum efficiency. The output torque and flux of the
machine in the two schemes are presented and compared.
KEYWORDS
1. Direct
Torque Control
2. Induction
Motor
3. Flux
Optimzation
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Figure
1: Block Diagram of Conventional DTC Scheme
Figure
2: Block Diagram of the Flux Optimized DTC Scheme
EXPECTED SIMULATION RESULTS
Figure
3: Stator d-q flux space vector without flux optimization
Figure
4: Stator d-q flux space vector with flux optimization
Figure
5: Variation of Stator Flux - Conventional DTC Scheme
Figure
6: Variation of Stator Flux - Optimized DTC Scheme
Figure
7: Variation of Mechanical Speed - Conventional DTC
Scheme
Figure
8: Variation of Mechanical Speed - Optimized DTC
Scheme
Figure
9: Electromagnetic Torque - Conventional DTC
Figure
10: Electromagnetic Torque - Optimized DTC
Figure
11: Percentage Efficiency of Flux Optimized DTC
CONCLUSION
In
this paper, DTC for an induction motor drive has been shown along with flux
optimization algorithm. DTC is a high performance, robust control structure. A
comparative analysis of the two DTC schemes, with and without flux optimization
algorithm has been presented. With flux optimization implementation, it is
observed that the efficiency of the about 87% has been obtained. MATLAB
simulation of a 15 Hp IM drive has been presented to confirm the results.
REFERENCES
[1] Werner
Leonhard. Control of Electric Drives. Springer-Verlag Berlin Heidelberg,
1996.
[2] F.
Blaschke. “The Principle of Field Orientation as Applied to The New Transvector
Closed Loop Control System for Rotating Field Machines”. Siemens Review,
pages 217–220, 1972.
[3] K.
Hasse. “On The Dynamic Behavior of Induction Machines Driven by Variable
Frequency and Voltage Sources”. ETZ Archive, pages 77–81.,1968.
[4] I.
Takahashi and T Nogushi. “A New Quick Reponse and High Efficiency Control
Strategy of an Induction Motor”. IEEE Trans. Industry Applications, IA
-22:820–827, 1986.
[5] M.
Depenbrock. “Direct Self Control (DSC) of inverter-fed induction machines”. IEEE
Trans. Power Electronics, 3(4):420–429, 1988.
